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UBC Theses and Dissertations

An engineering approach to the simulation of gross damage development in composite laminates Floyd, Anthony Michael


It is challenging to predict the development of gross damage in polymer matrix composite (PMC) laminates accurately. Existing tools are not suitable for analyses of this sort; in general they predict initial failure but do not consider the post-failure behaviour, or they treat it in a relatively simple fashion. The accuracy of these tools often depends on the load case and material considered. A plane-stress continuum damage mechanics (CDM) constitutive model for gross damage development in PMC laminates has been developed previously by Williams et al. The model, CODAM, was implemented into a finite element analysis code and applied with considerable success to modelling crack growth in tension tests, and damage development in non-penetrating impact events. While sufficient for those specific applications, the model had several shortcomings including sensitivity to the size of elements, restrictions on the shape of stress-strain curve, an insufficient treatment of the characterization of the post-peak stress behaviour, and no consideration of the energy dissipated by individual elements. This work addresses these shortcomings. The most significant change is the inclusion of a technique that explicitly accounts for the energy dissipated by single elements. This change addresses strain localization, reducing the element-size dependency of the model, and improves on the physically based interpretation of the model parameters. By introducing the available fracture energy per unit area (GF) as a model parameter, characterizing the material in the post-peak stress regime (i.e., in gross damage states) becomes easier to understand and implement. Additionally, the description of the damage development has been generalized such that all the mathematical relationships are piece-wise linear, which allows for more flexibility and by allowing for concurrent, independent damage modes, increases the physical nature of the inputs. Other improvements including a generalization to three dimensions and the development of algorithms to treat penetrating impact events have been implemented but are not addressed in this thesis. The model has been exercised and validated in a number of applications. Damage development in unnotched, single edge notched, double edge notched, over-height compact tension, centre notched, and centre hole tension tests has been examined and compared to experiments. Additionally, the development of damage in two bending applications has been studied. The performance of the model in simulating structures of different sizes has been a focus of the work, and although the structural size effect in unnotched applications (which is mainly due to statistical effects) is not captured, the results show that CODAM is able to predict structural size effect in all notched tension applications.

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